Preparation of 1-bromo-1-heptyne
0.5 mole of 1-heptyne is added slowly to a solution of 0.5 mole ethylmagnesium bromide dissolved in 500 ml of anhydrous ether, and the mixture is kept boiling under reflux 2-3 hours until no more ethane is evolved. Then the reaction mixture is placed in a cooling-bath at -32° C and bromine is slowly dropped in, this reacting at once with precipitation of magnesium bromide. After 75% of 0.5 mole of bromine has been added, the mixture suddenly becomes deep yellow; addition of bromine is then stopped and the mixture is allowed to warm to room temperature, whereupon the magnesium bromide dissolves and a lower layer of magnesium bromide etherate separates. By hydrolysis with dilute hydrochloric acid, washing with saturated sodium carbonate solution and water, drying over sodium sulfate, and distillation (69° C/25 mmHg) yields 70% of 1-bromo-1-heptyne.
J. Amer. Chem. Soc, 59, 1307 (1937).